Structural geology . rrangement in far as the limestones have impurities in them, secondarysilicates are likely to develop, such as actinolite and tremolite,which by their arrangement may give the rock a cleavage. OBLITERATION OF TEXTURES BY ROCK FLOWAGE Recrystallization, the dominant process in rock flowage, tendstoward an increase in the size of grain, the segregation of mineralsinto bands, a uniformity in size and shape of the mineral particles,and the growth of new minerals such as mica or hornblende notpreviously existent in the rock. Previous textures are commonlydestroyed. B
Structural geology . rrangement in far as the limestones have impurities in them, secondarysilicates are likely to develop, such as actinolite and tremolite,which by their arrangement may give the rock a cleavage. OBLITERATION OF TEXTURES BY ROCK FLOWAGE Recrystallization, the dominant process in rock flowage, tendstoward an increase in the size of grain, the segregation of mineralsinto bands, a uniformity in size and shape of the mineral particles,and the growth of new minerals such as mica or hornblende notpreviously existent in the rock. Previous textures are commonlydestroyed. Bedding is locally not completely obliterated, becausealternation of beds of originally different mineralogic characterand texture determines to some extent the kinds and size of thesecondary mineral particles formed in these beds by rock a faint banding of dark or light minerals or of fine or coarseminerals may mark the original bedding in a schistose rock. (SeeFigs. 45, 46 and 47). 94 STRUCTURAL GEOLOGY. Fig. 45. Photomicrograph of micaceous and quartzose schist with cleavage de-veloped across original bedding, from Little Falls, Minn. A graywaeke-slate,in which the banding has been marked by difference in texture as well as incomposition, has been subjected to deformation, with the result that a cleavagehas been superposed at right angles to the original bedding. Originally thelonger diameters of the particles of the bedded rock were parallel to the bed-ding. Accompanying the development of flow cleavage most of the con-stituents of the rock have been recrystallized. The cjuartz particles shown inthe light band have been drawn out with their longer diameters nearly at rightangles to the former plane of their longer diameters, and abundant new micahas developed with its greater diameters and mineral cleavage normal to theplane of bedding. FLOW CLEAVAGE AND BEDDING 95
Size: 1584px × 1578px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1913
